This application is a 371 of PCT/JP99/02719 filed May 25, 1999.
1. Technical Field
The present invention relates to a thermosetting resin sheet molding compound having at least one continuous layer consisting of electrically conductive fibers with a short fiber length and being particularly excellent in terms of electromagnetic wave shielding capability and electric conductivity and a method of producing the same.
2. Background Art
Fiber-reinforced plastics (FRPs) that use unsaturated polyester resins have high productivity, in addition to having excellent mechanical strength, heat resistance, water resistance, and chemical resistance, and therefore, they are used as materials for outside panels and outside accessories, beginning with home fixtures, such as bath tubs, wash basins, etc., and also in the field of automobiles. Electromagnetic wave shielding capability has recently come into demand, even in FRP molded articles, because of problems with electromagnetic interference (EMI) and several electromagnetic wave shielding FRPs have already been developed. An example is applying paint with shielding performance to the surface of molded articles. Moreover, there is another example produced by forming an electrically conductive sheet by impregnating a nonwoven cloth with a thermosetting resin comprising metal powder and molding the sheet into one unit with an SMC (Japanese Laid Open-Patent Application No. 59-138439) and glass cloths or mats that have been given electric conductivity by coating with aluminum and molded as one unit with a thermosetting resin (Japanese Laid-Open Patent Application No. 60-179243). However, there are problems with such methods in that breaking and elongation of the electrically conductive fiber layer occur during molding, thereby resulting in shorting of the electrically conductive layer, a reduction in density and non-uniformity. Proposals have been made to solve this disadvantage. In Japanese Patent Publication No. 3-70628, there is proposed molded articles produced by overlapping a glass fiber layer of short fibers impregnated with unsaturated polyester resin, a mat layer (middle layer) of electrically conductive fibers impregnated with unsaturated polyester resin, and a glass fiber layer (glass cloth) of long fibers and molding them under heat and compression.
However, by means of this method as well, the electrically conductive layer is formed from an electrically conductive mat and therefore, for instance, when a molded article of a complex shape is molded, stress is applied as a result of deformation of the electrically conductive mat during molding and the electrically conductive layer eventually breaks down and becomes non-uniform. Therefore, this method is not satisfactory.
Under these circumstances, the purpose of the present invention is to present a thermosetting resin sheet molding compound with which molded articles with excellent electromagnetic wave shielding capability and electric conductivity can be obtained without causing breakage or non-uniformity, since the electrically conductive layer of the compound follows perfectly the shape even when the compound is formed into a molded article with a complex shape.
As a result of intense studies, the inventor completed the present invention upon discovering that forming a continuous layer of electrically conductive fibers consisting of short fibers of a specific length is effective.
That is, the present invention relates to
(1) a thermosetting resin sheet molding compound, comprising at least one continuous layer of electrically conductive fibers with a fiber length of 50xcexcxcx9c5 mm;
(2) a thermosetting resin sheet molding compound according to the above-mentioned item(1) wherein the continuous layer of electrically conductive fibers is bonded as one unit with a reinforcement layer impregnated with a thermosetting resin composition;
(3) a thermosetting resin sheet molding compound according to the above-mentioned item (1) or (2), wherein an electrically conductive powder is uniformly dispersed throughout the entire molding compound;
(4) a thermosetting resin sheet molding compound according to any one of the above-mentioned items (1) through (3), wherein the continuous layer of electrically conductive fibers is formed by causing a thermosetting resin composition which comprises electrically conductive fibers, or electrically conductive fibers and electrically conductive powder mixed therein to penetrate into a reinforcement layer with;
(5) a method of producing the thermosetting resin sheet molding compound according to the above-mentioned item (1), comprising the step of forming at least one continuous layer of electrically conductive fibers with a fiber length of 50xcexc to 5 mm adjacent to a reinforcement layer impregnated with a thermosetting resin composition;
(6) a method of producing a thermosetting resin sheet molding compound according to any one of the above-mentioned items (1) through (3), comprising the step of causing a thermosetting resin composition which comprises electrically conductive fibers having a fiber length of 50xcexcxcx9c5 mm, or electrically conductive fibers and electrically conductive powder mixed therein, to penetrate into a reinforcement layer with; and
(7) a molded article, wherein the molding compound according to any one of the above-mentioned items (1) through (4) is cured in a mold.